This invention relates to a flow sensor particularly adapted to the measurement of fuel flow to internal combustion engines.
The broad concept of a flow sensor utilizing an annular raceway having an inlet, an outlet and a sensing means for recording the rate of rotation of a ball in the raceway has been disclosed in prior patents such as U.S. Pat. Nos. 818,566 and 3,861,210. However, such flow sensors previously known were unable to measure flow rates accurately across the wide range of flow rates, as for example, in automotive engines. That is, such prior flow sensors were relatively accurate at high engine speeds, but were not accurate at engine idle speed. A further problem concerning flow sensors for automotive engines arose due to the uneven fuel pressures of the fuel pump. Such pressure may vary per cycle between 0 and 8 pounds while the engine speed may vary between 500 RPMs and 10,000 RPMs. Heretofore, this caused irregular movement of the ball which contributed to inaccurate flow measurements. Also, with some previous flow sensor devices, the accumulation of trapped air in the raceway also diminished its performance.
It is therefore a general object of the present invention to provide an improved flow sensor that overcomes the problems and deficiencies indicated above.
Another object of the invention is to provide a flow sensor particularly suited to the wide range of operating conditions inherent in automotive engines.
A further object of the invention is to provide a flow sensor including an annular raceway for a counter ball wherein the fuel inlet to the raceway and fuel outlet from the raceway are disposed more than 360.degree. apart so that a continuous rotating force is applied to the counter ball throughout its path in the raceway even though the velocity of the fuel may vary over extreme ranges.
Another object of the invention is to provide a flow sensor with an annular raceway for a counter ball that will allow any air that may enter the raceway to escape through the outlet without being trapped therein and impeding the normal movement of the ball in the fluid stream.
Yet another object of the invention is to provide a flow sensor as indicated in the other objects wherein a variable volume chamber is interposed between the fluid inlet of the sensor and the raceway which under high flow is expanded and under low flow is contracted to provide a momentary source of fluid augmenting the fluid received as low flow is initiated to insure continued movement of the counter ball.